Liquid ejection head substrate and liquid ejection head

Abstract

An object is suppressing the reduction in the gas barrier property in a case where the cavitation resistance layer becomes thin. An embodiment of the present invention is a liquid ejection head substrate, including: a first layer that forms a heating element that generates heat energy to eject a liquid; a second layer that functions as an electric wiring connected with the heating element; a third layer that is insulative and covers the first layer and the second layer; and a fourth layer that is a layer arranged over the third layer so as to cover at least the heating element, formed of metal, and to generate an electrochemical reaction with the liquid, in which a first average crystal particle diameter on a side that is in contact with the liquid and a second average crystal particle diameter on a side of the third layer are different.

Dependencies are inferred from the claim text.